Plant genomes contain relatively large amounts of the modified nucleotide 5-methylcytosine (5.sup.m C) (Y. Greenbaum, et al., Nature 292: 850 (1981)). Despite evidence implicating cytosine methylation in plant epigenetic phenomena, such as repeat-induced gene silencing (TIGS), cosuppression, and inactivation of transposable elements (F. F. Assaad, et al., Plant Mol. Biol. 22: 1,057 (1993); C. Napoli, et al., Plant Cell 2: 279 (1990); J. Bender et al., Cell 83: 725 (1995); P. S. Chomet, et al., Genetics 138: 213 (1994); R. A. Martienssen, et al., Curr. Opin. Genet. Dev. 5: 234 (1995); M. A. Matzke, et al., Plant Physol., 107: 679-685 (1995)), the role of cytosine methylation in plant developmental processes is not clear.
In Arabidopsis, ddm mutants (decrease in DNA methylation) have been isolated with reduced levels of cytosine methylation in repetitive DNA sequences, although these mutations do not result in any detectable change in DNA methyltransferase enzymatic activity (A. Vongs, et al., Science, 260: 1,926 (1993), T. Kakutani, et al., Nucleic Acids Res. 23: 130 (1995)). After several generations of self-pollination, ddm mutants exhibit a slight delay (1.7 days) in flowering, altered leaf shape, and an increase in cauline leaf number (T. Kakutani, et al. (1995)).
The exact mechanisms that mediate plant development are presently not well understood. Plants that have an increased rate of development would be highly useful in plant breeding programs. Specifically, numerous plants, such as tree species, have extremely long generation times and therefore the number of crosses that can be generated within a given year or plant cycle is limited. In one extreme case, certain species of bamboo flower only once every one hundred years. Methods which could be used to decrease the maturation time would be highly beneficial in breeding programs involving many plants.
A reduction in the rate a plant matures can be used to increase the biomass production of a given plant. For numerous plants, increases in biomass yields would increase the economic value of the commercial plant. For example, flax, tobacco, alfalfa, spinach, lettuce, etc.
It is therefore the focus of the present invention to provide methods for increasing or decreasing the time required for a plant to mature as well as plants which are produced by these methods.
All references disclosed throughout this application are hereby incorporated by reference in their entirety.